The rules of cricket
Law 13 (The follow-on)
1. Lead on first innings
(a) In a two innings match of 5 days or more, the side which bats first and leads by at least 200 runs shall have the option of requiring the other side to follow their innings.
(b) The same option shall be available in two innings matches of shorter duration with the minimum required leads as follows:
(i) 150 runs in a match of 3 or 4 days;
(ii) 100 runs in a 2-day match;
(iii) 75 runs in a 1-day match.
A captain shall notify the opposing captain and the umpires of his intention to take up this option. Law 10.1(e) (Insufficient time to complete rolling) shall apply.
3. First day's play lost
If no play takes place on the first day of a match of more than one day's duration, 1 above shall apply in accordance with the number of days remaining from the actual start of the match. The day on which play first commences shall count as a whole day for this purpose, irrespective of the time at which play starts.
Play will have taken place as soon as, after the call of Play, the first over has started.